A Quick Guide to Band Pass Filters

Anyone who has ever been blindsided by RF interference caused by nearby transmitting stations while operating on Field Day or during a multi-radio contest should become well acquainted with our Word of the Day—Band Pass Filter.

There’s no doubt that even mild intrastation interference can cast a long shadow over an otherwise successful event, especially in a competitive environment when every station needs to be functioning at full capacity. In multi-radio contesting situations with mono-band operations, band pass filters can be used to specifically limit the RF band pass to a single amateur band—eliminating image and harmonic RF interference. Used with a transmit multiplexer, these passive filters provide additional isolation that enables multiple transceivers to be operated on different bands simultaneously on the same antenna. Use of a multiplexer (duplexers to pentaplexers are available from Low Band Systems) spares operators time and installation hassles as well as the cost of buying extra antennas and coax cable.

Available from DX Engineering, Low Band Systems offers HF Transmit Band Pass Filters for each of the ten HF Amateur Bands in 200, 500, and 1,500 watts models, and 2,000 watt models for 160, 80, 40, 20, 15, and 10 meters. The 1,500 and 2,000 watt versions are available with cooling fans. The units provide:

• Over 60 dB of out-of-band suppression that virtually eliminates out-of-band noise and interfering signals
• Sharp roll-off just outside each Amateur band; just below 3.5 MHz and just above 4.0 MHz for the 80 meter filter, for example
• Dramatically lower noise floor for enhanced single-band weak signal reception desired for elite contest and Field Day operations

It’s not too early to start thinking about Field Day 2020 (June 27-28). DX Engineering’s Triplexer Filter Combination Packages include Low Band Systems’ innovative 200W Triplexer (LBS-PB-TP200), LBS 20/15/10M band-pass filters, and coaxial cable jumpers. Choose from RG8X cable or high-performance RG400. 

Also check out SureFire Radio’s BF-100 Band Pass Filter System, which contains six high-performance bandpass filters in one compact package, covering the major contesting bands 160, 80, 40, 20, 15, and 10 meters.